Method and apparatus for perspective inversion

ABSTRACT

A surgical instrument navigation system is disclosed that allows a surgeon to invert the three-dimensional perspective of the instrument to match their perspective of the actual instrument. A data processor is operable to generate a three-dimensional representation of a surgical instrument as it would visually appear from either of at least two different perspectives and to overlay the representation of the surgical instrument onto an image data of the patient. The image data and the representations can be displayed on a display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/188,972, filed on Jul. 25, 2005, now U.S. Pat. No. 7,630,753, whichis a continuation of U.S. patent application Ser. No. 10/087,288 filedon Feb. 28, 2002, now U.S. Pat. No. 6,947,786. The disclosures of theabove applications are incorporated herein by reference.

FIELD

The present teachings relate generally to surgical instrument navigationsystems and, more particularly, to a navigation system that providesperspective inversion of the surgical instrument.

BACKGROUND

Modern diagnostic medicine has benefited significantly from radiology.Radiation, such as x-rays, may be used to generate images of internalbody structures. In general, radiation is emanated towards a patient'sbody and absorbed in varying amounts by tissues in the body. An x-rayimage is then created based on the relative differences of detectedradiation passing through the patients' body.

Surgical navigation guidance can provide a tool for helping thephysician perform surgery. One known technique involves trackingposition in real-time of a surgical instrument in the patient's anatomyas it is represented by an x-ray image. The virtual representation ofthe surgical instrument is a three-dimensional object superimposed ontothe two-dimensional image of the patient. Thus, the three-dimensionalrepresentation appears to be directed into or out of the two-dimensionalimage of the patient. An exemplary surgical navigation guidance systemis disclosed in U.S. application Ser. No. 09/274,972 filed on Mar. 23,1999 which is assigned to the assignee of the present teachings andincorporated herein by reference.

When an image is acquired, it is acquired from a certain perspective orpoint-of-view. In the case of a C-arm imaging device, the perspective isdetermined by the orientation of the C-arm around the patient.Specifically, the perspective is along the line connecting the imagesource and the image receiver. If the surgeon navigates the surgicalinstrument from the position of the image receiver, the perspective ofthe virtual representation of the instrument will match the surgeon'sperspective of the actual instrument. However, if the surgeon navigatesfrom the position of the radiation source, the perspective of thevirtual representation of the instrument will appear “flipped” from thesurgeon's perspective of the actual instrument.

Therefore, it is desirable to provide a surgical navigation system thatallows the surgeon to invert or “flip” the three-dimensional perspectiveof the instrument to match their perspective of the actual instrument.

SUMMARY

In accordance with the present teachings, a surgical instrumentnavigation system is provided that allows a surgeon to invert thethree-dimensional perspective of the instrument to match theirperspective of the actual instrument. The surgical instrument navigationsystem includes: a surgical instrument; an imaging device that isoperable to capture image data representative of a patient; a trackingsubsystem that is operable to capture in real-time position dataindicative of the position of the surgical instrument; and a dataprocessor adapted to receive the image data from the imaging device andthe position data from the tracking subsystem. The data processor isoperable to generate a three-dimensional representation of the surgicalinstrument as it would visually appear from either of at least twodifferent perspectives and to overlay the representation of the surgicalinstrument onto the image data of the patient. The navigation systemfurther includes a display that is operable to display therepresentation of the surgical instrument superimposed onto the imagedata of the patient.

For a more complete understanding of the teachings, reference may bemade to the following specification and to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a surgical instrument navigation system inaccordance with present teachings;

FIG. 2 is a diagram of an ideal and distorted image that may be capturedby the surgical navigation system;

FIGS. 3A and 3B illustrates the projective transformation processemployed by the surgical navigation system;

FIG. 4 is a flowchart depicting the operation of the surgical navigationsystem;

FIGS. 5A and 5B illustrate graphical representations of the surgicalinstrument superimposed onto a two-dimensional image of the patient;

FIG. 6 illustrates an exemplary graphical user interface of the surgicalinstrument navigation system; and

FIG. 7 is a flowchart depicting how perspective inversion isincorporated into the operation of the surgical instrument navigationsystem in accordance with the present teachings.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

FIG. 1 is a diagram of an exemplary surgical instrument navigationsystem. The primary component of the surgical instrument navigationsystem is a fluoroscopic imaging device 100. The fluoroscopic imagingdevice 100 generally includes a C-arm 103, x-ray source 104, x-rayreceiving section 105, a calibration and tracking target 106, andradiation sensors 107. Calibration and tracking target 106 includesinfrared reflectors (or alternatively infrared emitters) 109 andcalibration markers 111. C-arm control computer 115 allows a physicianto control the operation of imaging device 100, such as setting imagingparameters. One appropriate implementation of imaging device 100 is the“Series 9600 Mobile Digital Imaging System,” from OEC Medical Systems,Inc., of Salt Lake City, Utah. It should be noted that calibration andtracking target 106 and radiation sensors 107 are typically not includedin the Series 9600 Mobile Digital Imaging System; otherwise the “Series9600 Mobile Digital Imaging System” is similar to imaging system 100.

In operation, x-ray source 104 generates x-rays that propagate throughpatient 110 and calibration target 106, and into x-ray receiving section105. Receiving section 105 generates an image representing theintensities of the received x-rays. Typically, receiving section 105comprises an image intensifier that converts the x-rays to visible lightand a charge coupled device (CCD) video camera that converts the visiblelight to digital images. Receiving section 105 may also be a device thatconverts x-rays directly to digital images, thus potentially avoidingdistortion introduced by first converting to visible light.

Fluoroscopic images taken by imaging device 100 are transmitted tocomputer 115, where they may further be forwarded to computer 120.Computer 120 provides facilities for displaying (on monitor 121),saving, digitally manipulating, or printing a hard copy of the receivedimages. Three-dimensional images, such as pre-acquired patient specificCT/MR data set 124 or a three-dimensional atlas data set 126 may also bemanipulated by computer 120 and displayed by monitor 121. Images,instead of or in addition to being displayed on monitor 121, may also bedisplayed to the physician through a heads-up-display.

Although computers 115 and 120 are shown as two separate computers, theyalternatively could be variously implemented as multiple computers or asa single computer that performs the functions performed by computers 115and 120. In this case, the single computer would receive input from bothC-arm imager 100 and tracking sensor 130.

Radiation sensors 107 sense the presence of radiation, which is used todetermine whether or not imaging device 100 is actively imaging. Theresult of their detection is transmitted to processing computer 120.Alternatively, a person may manually indicate when device 100 isactively imaging or this function can be built into x-ray source 104,x-ray receiving section 105, or control computer 115.

In operation, the patient is positioned between the x-ray source 104 andthe x-ray receiving section 105. In response to an operator's commandinput at control computer 115, x-rays emanate from source 104 and passthrough patient 110, calibration target 106, and into receiving section105 which generates a two-dimensional image of the patient.

C-arm 103 is capable of rotating relative to patient 110, therebyallowing images of patient 110 to be taken from multiple directions. Forexample, the physician may rotate C-arm 103 in the direction of arrows108 or about the long axis of the patient. Each of these directions ofmovement involves rotation about a mechanical axis of the C-arm. In thisexample, the long axis of the patient is aligned with the mechanicalaxis of the C-arm.

Raw images generated by receiving section 105 tend to suffer fromundesirable distortion caused by a number of factors, including inherentimage distortion in the image intensifier and external electromagneticfields. Drawings representing ideal and distorted images are shown inFIG. 2. Checkerboard 202 represents the ideal image of a checkerboardshaped object. The image taken by receiving section 105, however, cansuffer significant distortion, as illustrated by distorted image 204.

The image formation process in a system such as fluoroscopic C-armimager 100 is governed by a geometric projective transformation whichmaps lines in the fluoroscope's field of view to points in the image(i.e., within the x-ray receiving section 105). This concept isillustrated in FIGS. 3A and 3B. Image 300 (and any image generated bythe fluoroscope) is composed of discrete picture elements (pixels), anexample of which is labeled as 302. Every pixel within image 300 has acorresponding three-dimensional line in the fluoroscope's field of view.For example, the line corresponding to pixel 302 is labeled as 304. Thecomplete mapping between image pixels and corresponding lines governsprojection of objects within the field of view into the image. Theintensity value at pixel 302 is determined by the densities of theobject elements (i.e., portions of a patient's anatomy, operating roomtable, etc.) intersected by the line 304. For the purposes of computerassisted navigational guidance, it is necessary to estimate theprojective transformation which maps lines in the field of view topixels in the image, and vice versa. Geometric projective transformationis well known in the art.

Intrinsic calibration, which is the process of correcting imagedistortion in a received image and establishing the projectivetransformation for that image, involves placing “calibration markers” inthe path of the x-ray, where a calibration marker is an object opaque orsemi-opaque to x-rays. Calibration markers 111 are rigidly arranged inpredetermined patterns in one or more planes in the path of the x-raysand are visible in the recorded images. Tracking targets, such asemitters or reflectors 109, are fixed in a known position relative tocalibration markers 111.

Because the true relative position of the calibration markers 111 in therecorded images are known, computer 120 is able to calculate an amountof distortion at each pixel in the image (where a pixel is a singlepoint in the image). Accordingly, computer 120 can digitally compensatefor the distortion in the image and generate a distortion-free, or atleast a distortion improved image. Alternatively, distortion may be leftin the image, and subsequent operations on the image, such assuperimposing an iconic representation of a surgical instrument on theimage (described in more detail below), may be distorted to match theimage distortion determined by the calibration markers. The calibrationmarkers can also be used to estimate the geometric perspectivetransformation, since the position of these markers are known withrespect to the tracking target emitters or reflectors 109 and ultimatelywith respect to tracking sensor 130. A more detailed explanation ofmethods for performing intrinsic calibration is described in thereferences B. Schuele et al., “Correction of Image IntensifierDistortion for Three-Dimensional Reconstruction,” presented at SPIEMedical Imaging 1995, San Diego, Calif., 1995 and G. Champleboux et al.,“Accurate Calibration of Cameras and Range Imaging Sensors: the NPBSMethod,” Proceedings of the 1992 IEEE International Conference onRobotics and Automation, Nice, France, May 1992, and U.S. applicationSer. No. 09/106,109, filed on Jun. 29, 1998 by the present assignee, thecontents of which are hereby incorporated by reference.

Calibration and tracking target 106 may be attached to x-ray receivingsection 105 of the C-arm. Alternately, the target 106 can bemechanically independent of the C-arm, in which case it should bepositioned such that the included calibration markers 111 are visible ineach fluoroscopic image to be used in navigational guidance. Element 106serves two functions. The first, as described above, is holdingcalibration markers 111 used in intrinsic calibration. The secondfunction, which is described in more detail below, is holding infraredemitters or reflectors 109, which act as a tracking target for trackingsensor 130.

Tracking sensor 130 is a real-time infrared tracking sensor linked tocomputer 120. Specially constructed surgical instruments and othermarkers in the field of tracking sensor 130 can be detected and locatedin three-dimensional space. For example, a surgical instrument 140, suchas a drill, is embedded with infrared emitters or reflectors 141 on itshandle. Tracking sensor 130 detects the presence and location ofinfrared emitters or reflectors 141. Because the relative spatiallocations of the emitters or reflectors in instrument 140 are known apriori, tracking sensor 130 and computer 120 are able to locateinstrument 140 in three-dimensional space using well known mathematicaltransformations. Instead of using infrared tracking sensor 130 andcorresponding infrared emitters or reflectors, other types of positionallocation devices which are known in the art may be used. For example,positional location devices based on magnetic fields, sonic emissions,or radio waves are also within the scope of the present teachings.

Reference frame marker 150, like surgical instrument 140, is embeddedwith infrared emitters or reflectors, labeled 151. As with instrument140, tracking sensor 130 similarly detects the spatial location ofemitters/reflectors 151, through which tracking sensor 130 and computer120 determine the three-dimensional position of dynamic reference framemarker 150. The determination of the three-dimensional position of anobject relative to a patient is known in the art, and is discussed, forexample, in the following references, each of which is herebyincorporated by reference: PCT Publication WO 96/11624 to Bucholz etal., published Apr. 25, 1996; U.S. Pat. No. 5,384,454 to Bucholz; U.S.Pat. No. 5,851,183 to Bucholz; and U.S. Pat. No. 5,871,445 to Bucholz.

During an operation, dynamic reference frame marker 150 is attached in afixed position relative to the portion of the patient to be operated on.For example, when inserting a screw into the spine of patient 110,dynamic reference frame marker 150 may be physically attached to aportion of the spine of the patient. Because dynamic reference frame 150is in a fixed position relative to the patient anatomy, and instrument140 can be accurately located in three dimensional space relative todynamic reference frame 150, instrument 140 can also be located relativeto the patient's anatomy.

As discussed above, calibration and tracking target 106 also includesinfrared emitters or reflectors 109 similar to those in instrument 140or dynamic reference frame 150. Accordingly, tracking sensor 130 andcomputer 120 may determine the three-dimensional position of calibrationtarget 106 relative to instrument 140 and/or dynamic reference frame 150and thus the patient position.

In general, the imaging system assists physicians performing surgery bydisplaying real-time or pre-acquired images, such as fluoroscopic x-rayimages, of the patient 110 on display 121. Representations of surgicalinstruments 140 are overlaid on pre-acquired fluoroscopic images ofpatient 110 based on the position of the instruments determined bytracking sensor 130. In this manner, the physician is able to see thelocation of the instrument relative to the patient's anatomy, withoutthe need to acquire real-time fluoroscopic images, thereby greatlyreducing radiation exposure to the patient and to the surgical team.“Pre-acquired,” as used herein, is not intended to imply any requiredminimum duration between receipt of the x-ray signals and displaying thecorresponding image. Momentarily storing the corresponding digitalsignal in computer memory while displaying the fluoroscopic imageconstitutes pre-acquiring the image.

FIG. 4 is a flowchart depicting the operation of the surgical navigationsystem. The physician begins by acquiring one or more fluoroscopic x-rayimages of patient 110 using imager 100 (step 400). As previouslymentioned, acquiring an x-ray image triggers radiation sensors 107,which informs computer 120 of the beginning and end of the radiationcycle used to generate the image. For a fluoroscopic x-ray imageacquired with imager 100 to be useable for navigational guidance, imager100, when acquiring the image, should be stationary with respect topatient 110. If C-arm 103 or patient 110 is moving during imageacquisition, the position of the fluoroscope will not be accuratelydetermined relative to the patient's reference frame. Thus, it isimportant that the recorded position of imager 100 reflects the trueposition of the imager at the time of image acquisition. If imager 100moves during the image acquisition process, or if imager 100 moves afterimage acquisition but before its position is recorded, the calibrationwill be erroneous, thereby resulting in incorrect graphical overlays. Toprevent this type of erroneous image, computer 120 may examine theposition information from tracking sensor 130 while radiation sensors107 are signaling radiation detection. If the calibration and trackingtarget 106 moves relative to dynamic reference frame 150 during imageacquisition, this image is marked as erroneous (Steps 401 and 402).

At the end of the radiation cycle, computer 120 retrieves the acquiredimage from C-arm control computer 115 and retrieves the locationinformation of target marker 106 and dynamic reference frame 150 fromtracking sensor 130. Computer 120 calibrates the acquired image, asdescribed above, to learn its projective transformation and optionallyto correct distortion in the image, (step 403), and then stores theimage along with its positional information (step 404). The process ofsteps 400-404 is repeated for each image that is to be acquired (step405).

Because the acquired images are stored with the positional informationof the calibration and tracking target 106 and dynamic reference frame150, the position of C-arm 103, x-ray source 104, and receiving section105 for each image, relative to patient 110, can be computed based uponthe projective transformation identified in the calibration process.During surgery, tracking sensor 130 and computer 120 detect the positionof instrument 140 relative to dynamic reference frame 150, and hencerelative to patient 110. With this information, computer 120 dynamicallycalculates, in real-time, the projection of instrument 140 into eachfluoroscopic image as the instrument is moved by the physician. Agraphical representation of instrument 140 may then be overlaid on thefluoroscopic images (step 406). The graphical representation ofinstrument 140 is an iconic representation of where the actual surgicalinstrument would appear within the acquired fluoroscopic x-ray image ifimager 100 was continuously acquiring new images from the same view asthe original image. There is no theoretical limit to the number offluoroscopic images on which the graphical representations of instrument140 may be simultaneously overlaid.

The graphical representation of the surgical instrument is athree-dimensional object superimposed onto a two-dimensional image ofthe patient. The three-dimensional representation of the instrument mayappear to be directed into or out of the two-dimensional image as shownin FIGS. 5A and 5B. In FIG. 5A, the tip 502 of the instrument 504 andthe projected length appear to be directed into the image. Conversely,in FIG. 5B, the tip 502 of the instrument 504 and the projected lengthappear to be coming out of the image.

When an image is acquired, it is acquired from a certain perspective orpoint-of-view. In the case of a C-arm imaging device 100, theperspective is determined by the orientation of the C-arm 103 around thepatient 110. Specifically, the perspective is along the line connectingthe image source 104 and the image receiver section 105. If the surgeonnavigates the surgical instrument from the position of the imagereceiver section 105, the perspective of the virtual representation ofthe instrument will match the surgeon's perspective of the actualinstrument. However, if the surgeon navigates from the position of theimage source 104, the perspective of the virtual representation of theinstrument will appear “flipped” from the surgeon's perspective of theactual instrument.

In accordance with the present teachings, the surgical instrumentnavigation system described above has been enhanced to allow a surgeonto invert the graphical representation of the instrument to match theirperspective of the actual instrument. In various embodiments, thenavigation system provides two possible perspectives: positive (+) ornegative (−). The positive state renders the instrument from theperspective of the image receiver section 105; whereas the negativestate renders the instrument from the perspective of the image source104. It is envisioned that either state may be designated the defaultstate. It is further envisioned that more than two perspectives may beavailable for selection by the surgeon.

Referring to FIG. 6, the perspective of the instrument is selectableusing a touch screen operable button 601 provided on the graphical userinterface of the navigation system. One skilled in the art will readilyrecognize that rendering a particular perspective of the instrument doesnot affect the profile of the instrument or the location of theinstrument on the image. The perspective selection only affects theinternal contours that give the instrument the appearance into or out ofthe image as shown in FIGS. 5A and 5B. Although a touch screen operablebutton is possible, it is envisioned that other techniques for selectingthe perspective of the instrument, such as a foot pedal or otherswitching device in close proximity to the surgeon, are also within thescope of the present teachings.

A more detailed description of how perspective inversion is incorporatedinto the operation of the surgical instrument navigation system isprovided in conjunction with FIG. 7. As noted above, the projection ofthe instrument into the fluoroscopic image is calculated in real-time asthe instrument is moved by the surgeon.

To do so, the tracking sensor 130, in conjunction with the computer 120,detects the position of the instrument 140 at step 702 relative to thedynamic reference frame 150, and thus relative to the patient 110. Thetracking sensor 130, in conjunction with the computer 120, alsodetermines the position of the tracking target 106 at step 704 relativeto the dynamic reference frame 150. Based this position data, thecomputer 120 can determine the position of the instrument 140 relativeto the tracking target 106 at step 706, and calibrate the position ofthe instrument relative to the image plane of the fluoroscopic images atstep 708.

Prior to rendering the image, the navigation system accounts for thevarious user settings 714, including instrument perspective. Theselected perspective setting 714 is input into the computer 120 at step710 which in turn provides corresponding input to the graphic renderingsoftware. One skilled in the art will readily recognize that other usersettings (e.g., zoom, rotate, etc.) may be accounted for by thenavigation system.

Lastly, the fluoroscopic image is rendered by the navigation system atstep 712. Specifically, the three-dimensional representation of thesurgical instrument is rendered from the perspective input by anoperator of the navigation system. The representation of the instrumentis then superimposed over the previously calibrated image data for thepatient. In this way, the perspective of the displayed instrumentmatches the surgeon's perspective of the actual instrument. As notedabove, the representation of the surgical instrument is tracked inreal-time as it is moved by the surgeon.

While the teachings have been described according to variousembodiments, it will be understood that the teachings are capable ofmodification without departing from the spirit of the teachings as setforth in the appended claims.

What is claimed is:
 1. A method for orienting a displayed representationof a surgical instrument while using a surgical instrument navigationsystem, comprising: operating the surgical instrument navigation systemto display a two-dimensional image of a patient that is based on anx-ray projection through the patient; operating the surgical instrumentnavigation system to track an instrument location of the surgicalinstrument relative to the patient; selecting a three-dimensionalgraphic rendering to represent the surgical instrument to besuperimposed on the displayed two-dimensional image, wherein thethree-dimensional graphic rendering is selected from one of a renderedfirst three-dimensional representation of the surgical instrument as thesurgical instrument would visually appear from a first perspective at aposition relative to the patient or a rendered second three-dimensionalrepresentation of the surgical instrument as the surgical instrumentwould visually appear from a second perspective that is different fromthe first perspective at the position relative to the patient, whereinthe selection is based on an actual operator perspective of the surgicalinstrument relative to the patient, wherein a profile of the graphicrendering is the same between the rendered first three-dimensionalrepresentation of the surgical instrument and the rendered secondthree-dimensional representation of the surgical instrument; and viewingthe selected three-dimensional rendering that represents the surgicalinstrument superimposed on the displayed two-dimensional image, whereinthe selected three-dimensional rendering that represents the surgicalinstrument is one of the rendered first three-dimensional representationor the rendered second three-dimensional representation; wherein thefirst perspective represents a first orientation of two possibleorientations of the surgical instrument relative to the patient and thesecond perspective represents a second orientation of the two possibleorientations of the surgical instrument relative to the patient.
 2. Themethod of claim 1, further comprising: inputting a selection into thesurgical instrument navigation system by an actual operator.
 3. Themethod of claim 1, wherein the first perspective is a perspective froman imager source.
 4. The method of claim 3, wherein the secondperspective is from an imager receiver.
 5. The method of claim 1,further comprising: selecting by an actual operator user settings of thesurgical instrument navigation system, including a zoom and a rotation.6. The method of claim 1, further comprising: detecting the position ofthe surgical instrument relative to a dynamic reference frame fixed tothe patient to determine the position of the surgical instrumentrelative to the patient; determining a display position of the surgicalinstrument for display relative to the displayed image datarepresentative of the patient based upon the detected position of thesurgical instrument relative to the dynamic reference frame; whereindisplaying the superimposed graphic on the displayed image includesdisplaying the superimposed graphic of the surgical instrument at thedetermined position of the surgical instrument relative to the patient,wherein the determined position relative to the patient is unchangedbetween the first perspective and the second perspective.
 7. The methodof claim 1, further comprising: determining a position of an imagingdevice including the image source that acquired the image data of thepatient relative to the dynamic reference frame; determining a positionof the surgical instrument relative to the imaging device based upon thedetermined position of the surgical instrument relative to the dynamicreference frame; and calibrating the determined position of the surgicalinstrument relative to an image plane of the image data representativeof the patient.
 8. The method of claim 1, wherein the selected graphicsuperimposed on the displayed image of the selected rendering of thefirst three-dimensional representation or the second three-dimensionalrepresentation only affects contours that give the respective renderedfirst three-dimensional representation or the rendered secondthree-dimensional representation of the surgical instrument anappearance into or out of the displayed image.
 9. A method for orientinga displayed representation of a surgical instrument while using asurgical instrument navigation system, comprising: operating thesurgical instrument navigation system to display a two-dimensional imageof a patient acquired from a first perspective of a x-ray imagereceiver; operating the surgical instrument navigation system to trackan instrument location of the surgical instrument relative to thepatient; selecting a three-dimensional graphical representation from oneof a first rendered three-dimensional graphical representation of thesurgical instrument at the instrument location at a first instrumentperspective relative to the patient and the x-ray image receiver or asecond rendered three-dimensional graphical representation of thesurgical instrument at the instrument location at a second instrumentperspective relative to a x-ray radiation source that is opposite thex-ray image receiver; and viewing on a display the selectedthree-dimensional graphical representation of the first renderedthree-dimensional graphical representation of the first instrumentperspective or the second rendered three-dimensional graphicalrepresentation of the second instrument perspective superimposed on thetwo-dimensional image at the tracked instrument location superimposed onthe two-dimensional image of the patient; wherein the profile is thesame and only contours are affected of the selected three-dimensionalgraphic representation superimposed on the displayed two-dimensionalimage between the first rendered three-dimensional graphicalrepresentation and second rendered three-dimensional graphicalrepresentation, wherein the contours give the respective first renderedthree-dimensional graphical representation or the second renderedthree-dimensional graphical representation of the surgical instrument afirst appearance that is inverted relative to a second appearancerelative to the displayed two-dimensional image.
 10. The method of claim9, wherein selecting the three-dimensional graphical representation isto match a user's perspective of the surgical instrument relative to thepatient in space.
 11. The method of claim 10, wherein selecting thethree-dimensional graphical representation is to allow the user toinvert the graphical representation of the surgical instrument.
 12. Themethod of claim 9, wherein the first instrument perspective is from thefirst perspective.
 13. The method of claim 9, further comprising:selecting the surgical instrument.
 14. The method of claim 13, whereinselecting the surgical instrument includes selecting a drill.
 15. Themethod of claim 9, further comprising: selecting at least onecharacteristic for displaying the three-dimensional graphicalrepresentation.
 16. The method of claim 15, wherein selecting the atleast one characteristic includes selecting at least one of anorientation, a zoom amount, a rotation, or combinations thereof.
 17. Themethod of claim 9, further comprising: calibrating an acquired imagedata to the patient, wherein the image data is used to generate thetwo-dimensional image.
 18. The method of claim 17, wherein calibratingthe image data to the patient includes transforming the image data tocorrect for at least one interference.
 19. The method of claim 9,further comprising: placing a dynamic reference frame on the patient;and wherein operating the surgical instrument navigation system to trackan instrument location of the surgical instrument relative to thepatient includes tracking the surgical instrument relative to the placeddynamic reference frame.
 20. The method of claim 9, wherein selectingone of the rendered tracked location of the surgical instrument includesmanually inputting into the surgical instrument navigation system theselected perspective.
 21. A method for orienting a displayedrepresentation of a surgical instrument while using a surgicalinstrument navigation system, comprising: viewing, by a user, adisplayed image including a two-dimensional image of a patient receivedfrom an x-ray imaging device; operating the surgical instrumentnavigation system to track a first instrument position of the surgicalinstrument relative to the patient; inputting, by the user, a firstselected perspective of the surgical instrument into the surgicalinstrument navigation system, wherein the selected perspective is anactual perspective of the surgical instrument as the surgical instrumentvisually appears from a perspective of the user relative to the patientwhen viewing the surgical instrument at a location of the user at thetracked first instrument position or a second selected perspective ofthe surgical instrument into the surgical instrument navigation system,wherein the second selected alternative perspective is different thanthe first selected perspective; viewing on a display device asuperimposed three-dimensional graphical rendering of the surgicalinstrument at the inputted first selected perspective or the secondselected perspective of the surgical instrument on the viewedtwo-dimensional image of the patient; and maintaining a profile of thethree-dimensional graphical rendering of the surgical instrumentsuperimposed on the displayed image to be the same between (i) theinputted first selected perspective and (ii) the inputted secondselected perspective; wherein only contours are effected between (i) thethree-dimensional graphical rendering of the surgical instrumentsuperimposed on the displayed image at the inputted first selectedperspective and (ii) the three-dimensional graphical rendering of thesurgical instrument superimposed on the displayed image at the inputtedsecond selected perspective to give the respective (i) three-dimensionalgraphical rendering of the surgical instrument superimposed on thedisplayed image at the inputted first selected perspective or (ii) thethree-dimensional graphical rendering of the surgical instrumentsuperimposed on the displayed image at the inputted second selectedperspective an appearance of into or out of the displayed image.
 22. Themethod of claim 21, further comprising: operating the surgicalnavigation system to operate a graphic rendering software to render theselected perspective.
 23. The method of claim 22, wherein inputting, bythe user, the first selected perspective or the second selectedperspective of the surgical instrument into the surgical instrumentnavigation system includes operating the surgical navigation system tooperate the graphic rendering software to render at least a firstthree-dimensional representation of the surgical instrument as thesurgical instrument would appear going into the viewed two-dimensionalimage and rendering and a second three-dimensional representation of thesurgical instrument as the surgical instrument would appear coming outof the viewed two-dimensional image.
 24. The method of claim 22, furthercomprising: operating the surgical instrument navigation system to tracka first position of the imaging device and tracking a second instrumentposition of the surgical instrument.
 25. The method of claim 24, furthercomprising: placing a dynamic reference frame on the patient; andwherein tracking the second instrument position of the instrumentincludes detecting the second position of the surgical instrumentrelative to the dynamic reference frame; wherein viewing on the displaydevice the superimposed three-dimensional graphical rendering of thesurgical instrument includes displaying the three-dimensional renderingof the surgical instrument at the detected second position of thesurgical instrument relative to the patient displayed on the displaydevice with the image data.
 26. The method of claim 25, furthercomprising: operating the surgical instrument navigation system tocalibrate the position of the surgical instrument relative to an imageplane of the displayed two-dimensional image based on image dataacquired with the imaging device and the tracked first position of theimaging device and the tracked second instrument position of thesurgical instrument.
 27. A method for orienting a displayedrepresentation of a surgical instrument while using a surgicalinstrument navigation system, comprising: viewing, by a user, adisplayed image including a two-dimensional image of a patient receivedfrom an x-ray imaging device; operating the surgical instrumentnavigation system to track a first instrument position of the surgicalinstrument relative to the patient; inputting, by the user, a selectedperspective of the surgical instrument into the surgical instrumentnavigation system, wherein the selected perspective is an actualperspective of the surgical instrument as the surgical instrumentvisually appears from a perspective of the user relative to the patientwhen viewing the surgical instrument at a location of the user at thetracked first instrument position; viewing on a display device asuperimposed three-dimensional graphical rendering of the surgicalinstrument at the inputted selected perspective of the surgicalinstrument on the viewed two-dimensional image of the patient; andmaintaining a profile of the three-dimensional graphical rendering to bethe same between a first selected perspective rendered three-dimensionalrepresentation of the surgical instrument and a second selectedperspective rendered three-dimensional representation of the surgicalinstrument; wherein the three-dimensional graphical renderingsuperimposed on the displayed image of the first selected perspectiverendered three-dimensional representation of the surgical instrument orthe second selected perspective rendered three-dimensionalrepresentation of the surgical instrument only affects contours thatgive the respective first selected perspective renderedthree-dimensional representation of the surgical instrument or thesecond selected perspective rendered three-dimensional representation ofthe surgical instrument an appearance into or out of the displayedimage.